Renewable resource as solar energy is critical to the future of our planet. Solar energy and the psychrometric energy (energy from air) obtained through an efficient heat recovery process known as Maisotsenko Cycle (herein further referred to as ‘M-Cycle’, e.g., see: Clean Air, Vol. 9, pp. 1-18, 2008 Copyright_2008 by Begell House, Inc.) can operate in synergy with each other and, together, they could provide an efficient solution for power generation, using 100% renewable energy. An advanced solar thermally driven power system proposed herein is a new alternative or non-conventional green technology for efficient producing power, which uses solar energy and air as a resource of renewable energy through the unique evaporative cooling process.
Today's market strongly needs to have a simple and cheap system for producing power (electricity), especially for residential applications, using renewable energy as solar heat and air.
The proposed solar thermally driven power system can help solving this problem by employing on the aforementioned processes for heat transfer (also solar heat) for generating mechanical or electrical energy with a maximal thermal efficiency.
Recent developments in the solar energy industry have included proposals for utilizing solar energy for driving rotational equipment such as turbines. In this regard, turbine-driven generators are quite attractive for use in the conversion of solar thermal energy through the proposed invention because of a relatively high efficiency of turbo-machinery rotating groups, and because of a relatively long operating life of such equipment.
These proposed solar systems can use air to drive micro-turbines with modular, mass-produced components with minimal on-site deployment costs and few environmental impacts. It will be of great advantage to commercialize the proposed solar power systems at the market, particularly, since they can be installed practically in any accessible place and they don't require electricity and water. They can be useful for household and industrial applications. They have a high thermal efficiency (about 75%) with low capital investment, exploiting solar energy and air as power sources. The proposed advanced solar thermally driven power system can also be used to retrofit existing power systems for reducing the consumption of fossil fuel, and by conventional combustion power systems using solar thermal energy.
This invention relates to systems and methods for production of electrical or mechanical power by exploiting solar energy as a power source. The inventive solar system has a high effective capacity with low capital investment.
More specifically, this invention relates to solar atmospheric pressure turbine systems as power generating systems in an open loop layout, having a turbine driven by solar-heated air, and which is connected to an electric load, for example, for driving an electric generator.
Also, the inventive solar thermally driven power system comprises a unique humidifying air recuperator, which recovers a sensible and latent heat from a hot airflow discharged from a turbine, cooling and dehumidifying this air before introducing thereof into an exhaust compressor. Simultaneously this recuperator heats up and humidifies airflow before introducing thereof into the turbine using the M-Cycle.
The inventive system includes a solar heater which is exposed directly to solar radiation, which heater is supplied with airflow and provides a means for direct solar heating of the airflow, which airflow is then drawn into an expansion machine through the aforementioned humidifying air recuperator by the exhaust compressor.
The proposed advanced solar thermally driven power system may be active at periods of time wherein incoming solar radiation is insufficient to heat up the air therein to a desired temperature, for example during an early morning, evening, and night time.
The inventive system also can be used for modification of conventional combustion power systems for reducing the consumption of fossil fuel, as well as for modification of conventional solar radiation power systems.
Compared to the traditionally utilized forms of depleteable fuels (coal, oil, nuclear), solar energy represents a clean renewable form of energy. Various solar systems have been designed to capture the solar energy and use it in different applications.
For instance, there are known devices for directly converting solar energy into electricity such as solar photovoltaic panels, which convert incident solar energy into electricity to provide energy solutions with zero pollution or greenhouse gas emissions.
There are thousands of patents for this subject. Some of them are: U.S. Pat. Nos. 3,449,874; 4,245,895; 4,269,173; 4,574,535; 5,125,608; 5,961,099; 6,563,040; 2005/0109384; 2006/0124168; 2008/0066801; 2009/0038672; 2010/0095609; 2011/0277809; 2012/0216855; 8,429,861.
The solar photovoltaic panel, however, suffers two major disadvantages. First, the electrical energy output per area of a photovoltaic panel is very low so that a large number of relatively expensive solar photovoltaic panels must be utilized in order to generate an economically viable quantity of electricity. Conventional solar photovoltaic systems for producing electricity traditionally have an efficiency rate of only 12%-15%, the most efficient ones of 25-35%, i.e. they are expensive and not efficient. Therefore, using the proposed advanced solar thermally driven power system of the present invention, it is possible to increase thermal efficiency more than 2 times for producing power.
Also, the solar photovoltaic panels have a second disadvantage in that they do not provide power when there is little or no available solar energy, hence they may satisfactorily operate in cooperation with a utility grid to avoid power interruptions of energy consumers.
The proposed advanced solar thermally driven power system can provide power anytime when either solar radiation and/or fuel is available, and thusly can operate independent of a utility grid. While emissions are not zero, the system is clean and significantly reduces greenhouse gas emissions compared with traditional energy generating systems.
There are known solar systems for heating up water by solar energy. For example, U.S. Pat. No. 8,353,286 teaches such “Solar water heater and method”.
The heated water can be used directly for heating or it can be used to power a turbine which in turn rotates a generator to produce electricity. A disadvantage of solar-heated water turbine systems is that such systems are very expensive to produce. Furthermore, water turbine systems are closed systems which present another disadvantage that can be clearer understood as discussed below in contrast with the present invention.
Traditional solar power systems usually include photovoltaic panels that generate electricity directly from sunlight. On the other hand, conventional heating-based power systems and machinery typically use Brayton or Rankine cycles. The latter are currently competitive with the photovoltaic panels on a cost per kilowatt basis.
Recent developments in the solar energy industry have included proposals for utilizing solar energy for driving rotational equipment such as turbines or the like. In this regard, turbine-driven generators are quite attractive for use in the conversion of solar energy because of a relatively high efficiency of turbo-machinery rotating groups, and because of a relatively long operating life of such equipment.
For example, US Patent Application 20110283700 “SOLAR COMBINED CYCLE POWER SYSTEMS” teaches that such solar system comprises a concentrating dish and a solar receiver to utilize concentrated solar radiation for heating a first working fluid, and a first turbine configured for generating electricity based on the Brayton cycle. This solar system comprises at least one recovery power plant including a heat recovery unit configured for utilizing exhaust heat of the first turbine to heat a second working fluid, and a second turbine configured for generating electricity by the Rankine cycle. However, this known solar system has a low thermal efficiency, which is 22% at the highest. Also, this system is complicated and expensive, using a combined cycle. It comprises a lot of elements to implement the Brayton cycle (as a topping cycle) and simultaneously Rankine cycle (as a bottoming cycle).
Efficiency is extremely important in solar power systems as a means to reduce size and space, and ultimately drive down installation costs. This is a reason why today solar thermal systems almost aren't used for producing power (electricity).
The Japan Society of Mechanical Engineers published a paper: “Study on Utilization of Solar Thermal Energy by Inverted Brayton Cycle” by KANEKO, Ken-ichi and et al. (see Proceedings of thermal engineering conference, 2001, 297-298, 20011103).
This paper presents a study of the performance of a solar thermal power generation system that has been working on the atmospheric pressure. The Heat Transfer Salt (HTS) was used as heat storage material heated by focusing solar energy through a convex lens. It was shown that if a high temperature HTS of more than 300 degree centigrade was developed, this solar thermal power generation system was characterized with only 30% of thermal efficiency.
The solar absorber typically comprised a device for transferring the concentrated solar radiation energy to a high temperature/high pressure working fluid by means of a relatively complex heat exchanger. The high pressure working fluid in turn was expanded through a high pressure turbine for conversion to rotational energy for driving electrical generators or the like (see, for example, U.S. Pat. No. 4,033,118 of this type of system). However, these systems have not been widely used chiefly because of complexity and expensiveness of the heat exchanger, together with relatively large dimensions of the heat exchanger.
Some solar-powered systems have been proposed, which attempt eliminating the high pressure/high temperature heat exchanger used as a solar absorber. For example, U.S. Pat. No. 3,203,167, discloses an atmospheric pressure solar absorber for transferring heat energy to ambient air which is then injected into a high pressure turbo-compressor cycle by means of a supersonic jet pump. However, the requirement of the jet pump, together with the high pressures and temperatures required for operating the turbo-compressor rotating group, still result in a relatively expensive and complex system which has not been commercially accepted.
The Mackay's U.S. Pat. No. 4,280,327 describes a solar-powered turbine system that comprises a solar air heater, where air is heated generally at atmospheric pressure and the heated air is supplied directly to a rotatable turbine of the subatmospheric turbine system. The heated air generally at atmospheric pressure is expanded and cooled through the turbine to a subatmospheric pressure to convert the solar heat energy into power for rotationally driving the turbine. In turn, the turbine rotationally drives a system compressor, as well as power output means comprising an electrical generator or the like.
However, this solar-powered turbine system isn't efficient. The known system doesn't provide a means for humidifying the air before the turbine in a thermodynamically efficient manner and consequently cannot guarantee a high level of moisture for this air, using heat from the exhaust air stream after the turbine. Air with a higher air humidity ratio and temperature, entering the turbine, creates lower density air, which is better for volumetric turbine efficiency.